Is it an old wisteria or a young Wisteria? Young seed grown wisteria won't flower until they are around 7 years old i believe, the grafted ones should flower immediatly.
Just had a read through my copy of Peter Adams' The Art of Flowering Bonsai. It suggests that common causes for wisteria not flowering can be repotting too frequently and not letting them get pot bound to induce stress flowering. It suggests repotting every 5 years but only removing dead root back to living tissue, and leaving longer alive roots and coiling them in the pot rather than cutting back all long roots.
Also an option mentioned is to use a water bath with fertiliser to a depth of 25% the depth of the pot to reduce air penetration and induce stress flowering that way.
thanks Tim--- the largest was gifted me about ten yrs ago because it never flowered for them and has been repotted when I received it and once more since--have used bloom booster for the last couple of yrs-- so will be mindful of fert and pruning this season-- others smaller have been struck from this plant and also not flowered--- full sun in summer is problematic here even in a water tray.
Seedling wisterias can sometimes take way longer than 7 years to mature enough to flower. One of mine produced its first flower buds at 19 years old and both got killed by frost that year. It took another 3 years before actually flowering but has been regular since then.
Cuttings from mature plants can flower in 1-3 years because the wood is already mature. I have 'Double Dragon' cuttings about to flower after 3 years from cuttings, even though they have not had really good conditions over that time.
Cuttings from immature plants will still produce immature plants so will take longer to reach flowering age.
You can only provide the best opportunity for your wisterias to flower. You can't hasten maturity.
I am still not convinced that many of the things reputed to help wisteria flower are accurate. Often these reports are after just one year of a particular treatment and may just have coincided with the plant being mature and ready to flower but the growers are so excited they just have to share.
Wisteria grow lots of roots really fast. The pots will be packed with roots after a single season and I have found that keeping them in a water bath is a necessity to keep them alive rather than inducement to flower.
Keep giving your wisterias all the care and attention they require. Flowers will occur when the plant is ready.
If your wisteria is only producing runners it won't flower, similar to a lot of fruit trees they produce short flowering 'spurs' these can be induced to develop easily on W.floribunda with regularly pruning any runners back to 2-3 leaves throughout the growing season, W.sinensis can sometimes be induced to flower following the same routine but is not reliable, seed grown plants can start flowering at 5yrs or not flower after 40yrs!
The best information on growing pruning training any and all Wisteria and allied Milletia is Peter Valder's book, not bonsai focused but the methods are easily transferred into bonsai growing them.
I was listening to this last night and recently on the Bonsai Mirai podcast he interviewed Andrew Robson to talk about flowering and fruiting species. If you skip to about 48 min 30 sec from there they discus Wisteria and the how to's of them. Andrew makes it all sound so simple so maybe that is worth a listen.
He mentions how water hungry they are a believes it to be better to water the vine more often than to sit it in a tray and also says maybe more importantly is to feed them, he says he gives a liquid feed twice a week in conjunction with a form of solid slow release. It's probably worth sitting down with pen a pad and take notes of the specifics and timings. Also talks about defoliation and getting two flush of flowers out of them. I've not finished the podcast yet but it is interesting.